I read somewhere that formating 128gb card in fat 32 with software. Could allow it to work on unsupported device.

I have no idea if the issue is Android version or Hardware. To read higher than 32gb.

Can someone help me understand.

Thank you

Well, I believe it is possible to get 128GB micro-SD inside of a device that support 32GB storage but not all of them.
I had a Samsung Sidekick 4G, and I manage to get a 128GB micro-sd card slot in it, however, it was sort of unstable.

Amazon had the 128GB SDXC Samsung Evo Class 10 on sale recently for $40, so I snagged a couple. They work great in a Samsung Tab S 10.5, no problem recognizing them. I can check what the format is, Android added some folders when I mounted the cards the first time, I don't know if that was also a formatting procedure - I've never used an expansion card in the tablet before. But even after the Android mount/unmount, I loaded one up with .mp4 movies off the server and they played, even the ones larger than 4GB so it's not FAT32.

Just checked one in the HTPC and it's exFAT format. Wasn't sure what Android used.Edited by GnarlyCharlie - 3/14/16 at 3:13pm